The present invention relates to electrical isolators in which microtransformers provide power transfer from a first isolator loop to a second isolator loop.
The use of microtransformers for power transfer is disclosed, for example in US Patent Application Publication 2006/0120115 A1 by the present inventor, the disclosure of which is incorporated herein by reference. Such power conversion systems include a power transformer that causes power transfer between a powered primary circuit loop and an otherwise unpowered secondary circuit loop. The power transformer is a member of a switch controlled, oscillating tank circuit that ideally operates at high frequency to maintain efficiency. In the known designs, at least two cross-coupled switches are needed to maintain a sustainable oscillation. The tank switching frequency is limited by the size of the switches and the inductance for the windings of the power transformers. The parasitic capacitance increases as the switch size increases and can limit the tank switching frequency.
A feedback path is provided between the circuit loops to regulate operation of the primary circuit loop to ensure that the power delivered to the secondary circuit loop remains within predetermined norms. The feedback path includes a feedback switch, which is included in a current path from a supply voltage (VDD) to the tank. This feedback switch causes undesirable power dissipation in the circuit. Moreover, the feedback path typically operates at a frequency much lower than the desired switching frequency of the tank circuit.
Power conversion efficiency and power conservation are important considerations for power converter systems. Accordingly, the inventors identified a need in the art for a microtransformer-based power conversion system that increases tank switching frequency over known systems and reduces switch-based losses.